A direct earth coupled heat pump is one that has its refrigerant evaporator/condenser in direct thermal contact with the earth from which heat is either extracted from in the heating mode or is introduced to in the cooling mode of operation. Many attempts have been made in the past to develop successful direct coupled heat pumps for residential and commercial uses. These attempts have failed to adequately meet a number of requirements associated with an economically and functionally viable system. Some of the shortcomings include:
Inadequate oil return to the compressor primarily in the heating mode;
Inadequate evaporator length and spacing for properly extracting heat from the earth resulting in low capacity and low efficiency of the systems;
Lack of a proper means to store additional refrigerant required during the cooling operation, but not needed during the heating mode.
Lack of volume control of the compressor for providing the necessary increase in displacement during the heating operation over that displacement needed for the cooling operation. This lack of displacement control results in insufficient heating capacity during the coldest weather.